Power factor in power converters is defined as the ratio of the real power delivered to a load to the apparent power provided by a power source, and power converters should be able to deliver power from the power source to the load with high power factor.
Recently, government agencies gradually require power factors in power converters to exceed a certain minimum level by regulation. For example, Energy Star in U.S. requires power factors in power converter to achieve at least 87% if a specification of a device requires more than 49 W, such as notebooks. On the other hand, Energy Star in U.S. requires power factors in power converter to achieve no less than 68% if a specification of a device requires no more than 5 W, such as mobile phones.
Typically, power factor correction (PFC) is achieved through the use of specific analog integrated circuits (IC) especially designed for improving PFC in power converters. In addition, each of the aforementioned analog ICs varies in different application fields, thus lacking a generalized structure to adopt different designs in different application field.
For now, if a device requires more than 60 W, the function of PFC is usually achieved through the use of the aforementioned analog ICs in power converters. However, if a device requires no more than 65 W, the device usually does not have PFC function, since the price of power converters having the aforementioned analog ICs for improving PFC will be about or at least twice the price of power converters without PFC function.
In addition, the implementation of aforementioned conventional power converters usually requires complex circuitry further requiring considerable efforts to stabilize them. And once again, in different applications the power converters need to utilize different specific analog ICs to achieve high power factor correction.
In view of the above, there is a need for a power converter with non-complex circuitry that utilizes a common digital microcontroller that provides high PFC, and the digital microcontroller provides pulse width modulation (PWM) signal to control the power converter. The aforementioned digital microcontroller providing PWM signal is able to be regarded as a digital PWM controller.